【LeetCode热题100】【链表】两数相加

class Solution {
public:
    ListNode *addTwoNumbers(ListNode *l1, ListNode *l2) {
        ListNode *head = nullptr, *tail = nullptr;
        int carry = 0;
        while (l1 || l2 || carry) {
            int a = l1 == nullptr ? 0 : l1->val;
            int b = l2 == nullptr ? 0 : l2->val;
            int sum = a + b + carry;
            if (head == nullptr)
                head = tail = new ListNode(sum % 10);
            else {
                tail->next = new ListNode(sum % 10);
                tail = tail->next;
            }
            carry = sum / 10;
            if (l1)l1 = l1->next;
            if (l2)l2 = l2->next;
        }
        return head;
    }
};